5-Oxoproline (pyrrolidone carboxylic acid), a product of the enzymatic degradation of glutathione mediated by the gamma-glutamyl cycle, will be studied in order to establish its position as a normal intermediate in mammalian metabolism. Levels of this compound will be determined in tissues and physiological fluids, by the application of a new gas liquid chromatographic procedure coupled with electron capture detection. Patients with amino-acidurias, acquired and inherited disorders of amino acid metabolism and mental retardation frequently associated with these conditions, will be screened for abnormalities of metabolism of 5-oxoproline. Studies will be carried out on dogs to investigate the interrelationship between renal amino acid transport and the formation and excretion of 5-oxoproline in urine. Metabolic inhibitors will be used in experiments on rats and mice in order to evaluate the metabolic activity of the gamma-glutamyl cycle in various tissues and its relation to amino acid transport. The capacity of dogs to metabolize extraneous 5-oxoproline will be determined by measuring the rate of its disappearance from circulation and excretion in urine after an intravenous load. The metabolic products of 5-oxoproline in urine will be studied after an intravenous tracer dose of C14-labeled compound in dogs. Particular attention will be given to the time course of incorporation of the label into glutamate and its derivatives (glutamine and gamma-glutamyl amino acids).